1. Field of the Invention
The present invention pertains to a drive circuit for a semiconductor device and a semiconductor switching circuit using the drive circuit. Especially, the present invention pertains to a drive circuit for a semiconductor power device, which is turned on and off through controlling the current applied to its control electrode.
2. Description of the Related Art
A transistor disclosed in Japanese Published Unexamined Patent Application H6-252408 is known as xe2x80x9ca current-controlled semiconductor elementxe2x80x9d suitable for driving an inductive load. The transistor is supplied at its control electrode with a control current for turning on and off the transistor while its drain electrode is connected to the inductive load. The control electrode current is received from a CMOS inverter, which has a pMOS transistor and an nMOS transistor connected in series with each other. The CMOS inverter is thus connected between the controlled current source and the source electrode of the transistor. The control current is connected with a connecting point between the pMOS transistor and nMOS transistor. When the voltage Vm supplied to the input terminal of the CMOS inverter or the control electrodes of both the p-type and nMOS transistors is shifted from high level to low level, the pMOS transistor is turned on and the nMOS transistor is turned off. Accordingly, the carriers are injected into the control electrode, hence turning on the transistor to pass the current from the source to the inductive load. As the load connected to the transistor is of an inductive type, the drain current Ids is gradually increased. When the signal Vm at the driver signal input terminal turns to the high level, the pMOS transistor is turned off and the nMOS transistor is turned on. Accordingly, the current to the control electrode of the transistor is then disconnected. As the carriers are pulled out via the nMOS transistor from the control electrode of the transistor, they turn off the transistor.
However, the path along which the control current flows has, in addition to parasitic inductance, a level of resistance including the ON resistance of the nMOS transistor and the resistance of wire itself and a size of parasitic capacitance. The transistor is commonly a current driven device and thus draws a large amount of control current while it is turned off within a short period of time. It is hence necessary in the operation of turning off the release the energy accumulated in the parasitic inductance at once. This will result in RLC resonance between the energy and the parasitic components, thus oscillating the control electrode voltage Vgs. As the control electrode voltage is increased to an ON voltage level by the oscillation, it unfavorably turns the transistor on thus passing the drain current Ids. When the resistance of the carrier pull out circuit is increased for preventing the rapid pulling of control current, the oscillation of the control electrode voltage may be diminished more or less. However, the storage period from the release of a turn off command to the actual turning off of the transistor increases.
It is an object of the present invention to provide a drive circuit for a semiconductor device and a semiconductor switching circuit using the drive circuit, which minimize the oscillation of the control signal for turning off the semiconductor device.
Another object of the present invention is to provide a drive circuit and a semiconductor switching circuit using the drive circuit, by which high-speed turn off transition of the semiconductor device is carried out, sweeping out storage carries effectively and quickly in the semiconductor device, and its erroneous operation due to the unexpected oscillation of the control electrode voltage is successfully be prevented.
Still another object of the present invention is to provide a drive circuit and a semiconductor switching circuit using the drive circuit, in which a specific feature representing a turn-off transition of the semiconductor device is close to its completion is measured at higher accuracy.
Still another object of the present invention is to provide a drive circuit and a semiconductor switching circuit using the drive circuit, in which the response speed to the specific feature representing the turn-off transition of the semiconductor device is close to its completion is high.
Still another object of the present invention is to provide a drive circuit and a semiconductor switching circuit using the drive circuit, in which the resistance component which serves as a damping factor in the RLC resonance is increased so as to effectively attenuate the oscillation of the control electrode voltage, thus inhibiting the semiconductor device from being accidentally turned off.
Still another object of the present invention is to provide a drive circuit and a semiconductor switching circuit using the drive circuit, which can suppress the generation of voltage surges throughout the circuit, and improve the noise immunity.
Still another object of the present invention is to provide a drive circuit and a semiconductor switching circuit using the drive circuit, in which the switching element constituting the drive circuit is inhibited from being turned on by the impulses noise so as to protect the erroneous operation of the semiconductor device.
Still another object of the present invention is to provide a drive circuit and a semiconductor switching circuit using the drive circuit, in which an excessive large flow of unrequired current in the drive circuit due to the impulse noise can be effectively suppressed so as to protect the erroneous operation of the semiconductor device.
For achievement of the above objects of the present invention, a first feature of the present invention, pertaining to a drive circuit for a semiconductor device having a control electrode, first and second main electrodes, inheres in the circuit configuration having a detector, a carrier pull out circuit and a control circuit. The detector detects a specific feature representing a turn-off transition of the semiconductor device is approaching to its completion. The carrier pull out circuit pulls out stored carriers from the control electrode. The control circuit maintains the impedance of the carrier pull out circuit at a first level in the initial stage of the turn-off transition and, when the detector detects the specific feature, changes the impedance of the carrier pull out circuit to a second level higher than the first level.
A second feature of the present invention, pertaining to a semiconductor switching circuit, inheres in the circuit configuration having a semiconductor device, which has a control electrode, first and second main electrodes, a detector, a carrier pull out circuit and a control circuit. The detector detects a specific feature representing a turn-off transition of the semiconductor device is approaching to its completion. The carrier pull out circuit pulls out stored carriers from the control electrode. The control circuit maintains the impedance of the carrier pull out circuit at a first level in the initial stage of the turn-off transition and, when the detector detects the specific feature, changes the impedance of the carrier pull out circuit to a second level higher than the first level.
A third feature of the present invention, pertaining to a drive circuit for a semiconductor device having a control electrode, a first and second main electrodes, inheres in the circuit configuration having a detecting means. The detecting means is provided for detecting a specific feature representing a turn-off transition of the semiconductor device is approaching to its completion. The carrier pull out means is provided for pulling out stored carriers from the control electrode. The control means is provided for maintaining the impedance of the carrier pull out means at a first level in the initial stage of the turn-off transition and, when the detecting means detects the specific feature. And the control means is provided for changing the impedance of the carrier pull out means to a second level higher than the first level.
A fourth feature of the present invention, pertaining to a semiconductor switching circuit, inheres in the circuit configuration having a semiconductor device, which has a control electrode, first and second main electrodes, a detecting means, a carrier pull out means. The detecting means is provided for detecting a specific feature representing a turn-off transition of the semiconductor device is approaching to its completion. The carrier pull out means is provided for pulling out stored carriers from the control electrode. The control means is provided for maintaining the impedance of the carrier pull out means at a first level in the initial stage of the turn-off transition and, when the detecting means detects the specific feature. And the control means is provided for changing the impedance of the carrier pull out means to a second level higher than the first level.
Other and further objects and features of the present invention will become obvious upon an understanding of the illustrative embodiments about to be described in connection with the accompanying drawings or will be indicated in the appended claims, and various technical advantages not referred to herein will occur to one skilled in the art upon employing of the invention in practice.